Summary More than 70% of preterm infants are born between 34 and 36 completed weeks of gestation or late preterm. This is the equivalent of 8% of all infants born in the United States each year. These infants are at increased risk for morbidity and mortality in the perinatal period and are twice as likely to die in the first year of life. Despite this, only preliminary research has been done to explore the morbidity of these infants in the first year of life. Overarching hypothesis: Late preterm infants are at increased risk for morbidity beyond the perinatal period. Specific Aim 1: Describe the incidence and risk factors for late preterm delivery in a sociodemographically-diverse population using private and public administrative claims data linked to birth certificate records. Hypothesis: Race and socioeconomic status are independent risk factors for late preterm delivery. Dr. Halloran will link birth certificate records to private and public insurance claims data. She will describe the incidence and risk factors for late preterm birth among a racially- and economically-diverse group to increase the understanding of the inadequately-defined epidemiology of late-preterm births. Specific Aim 2: Evaluate cause-specific and gestational-age-specific morbidity in late preterm and term infants over the first year of life, specifically respiratory-related conditions. Hypothesis: Late preterm infants are twice as likely to have respiratory diagnoses, respiratory-related medication use, and respiratory-related hospitalizations compared to term infants. Dr. Halloran will characterize the association of gestational age with respiratory complications including respiratory-related diagnoses, inpatient/outpatient health care utilization, and medication use in late preterm versus term infants. Specific Aim 3: Determine the difference in cost of infant care in late preterm versus term infants in the first year of life using population-based data which includes private and public claims data linked to birth certificate records. Hypothesis: Late preterm infants have at least 100% increase in total cost of care during the first year of life compared to term infants. Dr. Halloran will examine the total cost (inpatient, outpatient, and prescription drugs) and system-specific cost in late preterm versus term infants throughout the first year of life. Following a research fellowship and Masters of Science in Public Health, Dr. Halloran is on the tenure-track in the Division of General Pediatrics at St. Louis University (SLU). She has chosen a multidisciplinary panel of mentors with expertise and experience in maternal-fetal medicine, neonatology, health services research, health economics, and biostatistics. This committee in combination with the support of the SLU School of Medicine, SLU School of Public Health, and Washington University Institute of Clinical and Translational Science will provide her with a strong research environment. Through advanced statistical training as part of a PhD in Outcomes Research and the mentorship of a diverse, experienced group of mentors and advisors, Dr. Halloran will be well-positioned to become an independent investigator in infant outcomes research. PUBLIC HEALTH RELEVANCE: This proposal will lead to the development a risk-based system to sub classify the heterogeneous category of late-preterm infants and improve the precision of risk assessment in this population. This project will lay the groundwork for future studies designed to improve the health of late preterm infants who account for 8% of all infants born in the US each year - through additional prospective research or interventions. It will provide the training and experience necessary for Dr. Halloran to become an independent investigator in infant outcomes research.